D-V09

Signalment (JPC #1788178): Yearling heifer

HISTORY: This heifer had protracted bloody diarrhea. Gross lesions were noted in the oral cavity, the esophagus, rumen, and small and large intestines.

HISTOPATHOLOGIC DESCRIPTION:

SLIDE A: Colon: The mucosa is diffusely thin, there is multifocal erosion of the superficial mucosal epithelium, and there is necrosis/loss of 50% of the colonic glands with replacement by hemorrhage, fibrin, edema, moderate numbers of viable and necrotic neutrophils, macrophages, fewer lymphocytes, and plasma cells. The remaining colonic glands are ectatic, dilated up to 250 µm, lined by attenuated epithelium, and contain low to moderate numbers of degenerate and viable neutrophils, macrophages, sloughed epithelial cells, necrotic cellular and karyorrhectic debris, and fibrin (crypt abscesses). Less affected glands exhibit loss of mucous cells. Multifocally, ectatic glands extend into or through the muscularis mucosa and into the submucosa (crypt herniation). The submucosa contains previously described inflammatory cells in low to moderate numbers and mild hemorrhage, fibrin, and edema with dilated lymphatics, and there is an absence of lymphoid tissue. There is multifocal mesothelial cell hypertrophy. Necrotic debris and previously mentioned inflammatory cells are also present within the colonic lumen.

SLIDE B: Esophagus: Affecting 40% of the mucosa with variable extension to the submucosa, there are multifocal, well demarcated, segmental areas of mucosal erosion and necrosis affecting the stratum corneum and stratum granulosum, and extending into the stratum spinosum; changes are characterized by loss of epithelium with replacement by necrotic debris, many degenerate neutrophils which occasionally form discrete aggregates, low numbers of eosinophils and lymphocytes, and mild hemorrhage, fibrin, and edema. Adjacent to areas of erosion, epithelial cells have pale swollen, vacuolated cytoplasm (degeneration) or are shrunken and hypereosinophilic with pyknotic or karyolitic nuclei (necrosis) and few transmigrating neutrophils. The superficial submucosa is mildly expanded by edema and low numbers of neutrophils, lymphocytes, and plasma cells.

Lymph node: Subcapsular and medullary sinuses are moderately expanded by increased numbers of draining macrophages, neutrophils, fewer eosinophils, and fibrin. In the hilus, a medium-sized artery exhibits recanalization.

MORPHOLOGIC DIAGNOSIS: 1. Colon: Colitis, erosive and necrotizing, subacute, diffuse, severe, with crypt abscesses, crypt herniation, and marked transmural edema, breed unspecified, bovine.

2. Esophagus: Esophagitis, erosive and necrotizing, subacute, multifocal, moderate.

3. Lymph node: Sinus histiocytosis, diffuse, moderate.

ETIOLOGIC DIAGNOSIS: Pestiviral colitis and esophagitis

CAUSE: Bovine pestivirus

CONDITION(S): Bovine viral diarrhea; mucosal disease

GENERAL DISCUSSION:

Bovine viral diarrhea virus (BVDV) is of the genus Pestivirus, family Flaviviridae, and is a small, enveloped RNA virus
Susceptible species to BVDV infection include cattle, pigs, sheep, goats, bison, captive and wild cervids, and Old World and New World camelids
The majority of BVDV infections, regardless of infecting strain type, result in asymptomatic infections that largely go undetected
Genotypes:

BVDV is taxonomically divided into BVDV1 and BVDV2 genotypes, both of which contain cytopathic (CP) and noncytopathic (NCP) biotypes
- Within the U.S. cattle population there are 3 major subtypes: BVDV1a, BVDV1b, and BVDV2a; the BVDV1b subtype predominates
BVDV3, known as HoBi-like pestivirus or atypical pestivirus, is found in South America, Asia, and Europe; it is genetically and antigenically similar to BVDV, and causes similar disease

Biotypes:

BVDV is subdivided into cytopathic (CP) and noncytopathic (NCP), referring to virus activity in vitro, not in vivo

CP- causes cellular vacuolation and apoptosis in tissue culture
NCP- causes inapparent persistent infection in cultured cells

NCP isolates account for approximately 90% of BVDV isolates
By recombination of RNA the more common NCP can shift biotype to CP
- Recombination results in splitting of the NS2-3 protein to NS3, a marker for CP BVDV

Outcome of infection depends on viral strain and virulence, whether or not the host is immunotolerant or immunocompetent to BVDV, whether or not the animal is pregnant, and if so, the stage of pregnancy, and concurrent level of stress at the time of infection
The two most clinically severe forms of BVD are mucosal disease (MD) in persistently infected (PI) animals and severe acute BVD caused by very virulent virus strains

PATHOGENESIS:

Virus is shed in fluids: Saliva, blood, oculonasal discharge, urine, feces, semen, uterine secretions, amniotic fluid, and fetal tissue
- Virus outer membrane proteins E1 and E2 may act as attachment proteins
- Receptor mediated endocytosis to target cells possibly through: Clathrin, lysosomal-associated membrane protein-2, mannose receptors
Transmission is via ingestion or inhalation with primary replication occurs in tonsils and oropharyngeal lymphoid tissue (Waldeyer’s ring)
- Lymphoid cells initially proliferate but undergo massive lysis once viral replication occurs
BVDV targets lymphocytes and macrophages; enters circulating monocytes and is transported to lymphoid tissues and the subepithelial connective tissue of the dermis and GI tract, where it spreads locally to overlying epithelial cells
- Possible outcomes of infection include: Fetal infection (depends on stage of gestation at time of infection but can result in early embryonic death, abortion, persistent infection (PI), congenital abnormalities), classical BVD, severe acute BVD, mucosal disease

Fetal infection

Transplacental infections – How BVDV affects the fetus:
- Infection during 50-100 days gestation: Fetal death, abortion, mummification
- Infection during 100-150 days gestation: Congenital defects such as microencephaly, hypomyelinogenesis, cerebellar hypoplasia and dysgenesis, hydranencephaly, hydrocephalus, defective myelination of the spinal cord; other lesions include microphthalmia, cataracts, retinal degeneration, atrophy and dysplasia, optic neuritis, thymic aplasia, hypotrichosis, alopecia, brachygnathia and other skeletal abnormalities, growth restriction, and pulmonary hypoplasia

Osteopetrosis due to decreased osteoclasts and impaired bone formation
Mechanism for cerebellar hypoplasia: BVDV infects the developing germinal cells of the cerebellum and kills Purkinje cells in the granular layer, resulting in necrosis and inflammation

Infection prior to 125 days of gestation with NCP strain: If the calf survives, it may develop immunotolerance and persistent infection (PI)

Bovine fetuses become immunocompetent at 150-200 days of gestation

Persistent infection (PI)

PI calves may be normal, weak, or undersized at birth and most succumb to mucosal disease (MD) between 6 month to 2 years of age
Survivors are viremic (but seronegative) and shed virus constantly thus are the most important source of infection for other cattle

Mucosal disease (MD)

Pathogenesis: In utero infection (prior to gestation day 125) with NCP strain > immune tolerance and PI > eventual infection with CP strain or RNA recombination of the NCP persistent virus > overwhelming infection with little/no immune response > mucosal disease > death usually within two weeks
Characterized by low morbidity but high mortality
Acute and chronic mucosal disease can occur; if the animal survives the acute form and does not die in the expected time frame, they develop chronic symptoms; these cattle are unthrifty with intermittent diarrhea, chronic bloat, decreased appetite, weight loss, interdigital erosions, or nonhealing erosive skin lesions; persistent ocular and nasal discharges are common; alopecia and hyperkeratinization of the skin, typically in the neck, back and perineal areas; chronic lameness due to coronitis, or even laminitis can develop; these chronically affected animals usually die within 18 months due to severe debilitation

Classical BVD

Immunocompetent animals over six months may develop classical BVD
Usually due to NCP BVDV
Transient high morbidity low mortality
Fever, mild oculonasal discharge, and mild oral erosions and ulcers
Affected animals are probably immune for life

Severe Acute Bovine Viral Diarrhea:

Characterized by high morbidity and high mortality in all age groups of susceptible animals and has a peracute to acute course with fever, sudden death, diarrhea, or pneumonia
Usually due to BVDV type 2; can be seen with BVDV-1b
Can be associated with thrombocytopenic syndrome with epistaxis, hyphema, mucosal hemorrhage, bloody diarrhea

TYPICAL CLINICAL FINDINGS:

Acute BVD: In the mild form, there is transient fever, neutropenia with no left shift, thrombocytopenia, mild depression, inappetence, drop in milk production, oculonasal discharge, and diarrhea
Severe acute BVD: high morbidity and mortality in all age groups; peracute to acute course: with fever, sudden death, diarrhea, or pneumonia
MD: Pyrexia, depression, weakness, lameness, anorexia, dehydration, hypersalivation, mucopurulent nasal discharge, lacrimation, profuse watery diarrhea with tenesmus (tenesmus causes the “tiger stripe” colonic lesions)

TYPICAL GROSS FINDINGS:

Acute BVD: In the mild form, mild erosions or shallow ulcerations of the muzzle and oral cavity; Peyer’s patches outlined by coagulated blood and overlain by fibrin; fibrinohemorrhagic typhlocolitis
Severe acute BVD: Lesions closely resemble mucosal disease (below)
MD:

Linear esophageal ulcerations
Erosions and ulcerations of mouth, tongue, oral and ruminal papillae, reticulum, omasum, abomasum, cecum/colon
“Tiger stripe” colonic lesions
Peyer's patches swollen, necrohemorrhagic, +/- diphtheritic membrane
Erosive-ulcerative interdigital dermatitis and coronitis
Recent report of MD lacking intestinal lesions (Bianchi, Vet Pathol. 2017)

TYPICAL LIGHT MICROSCOPIC FINDINGS:

Peyer’s patches: Severe, acute inflammation in overlying intestinal mucosa with crypt herniation; destruction of underlying glands; collapse of lamina propria; lymphocytolysis
Distal small and large intestine: Destruction of epithelial lining of intestinal crypts
Hyaline degeneration or fibrinoid necrosis of blood vessels (submucosal and mesenteric arterioles); vasculitis in multiple organs accompanied by a mild-to-moderate mononuclear cell infiltrate in the vessel walls and perivascular tissues
Mesenteric lymph nodes and spleen: Lymphocytolysis and lymphoid depletion
Erosions in the skin are similar to those seen in the intestinal mucosa and there is hyperkeratosis in chronic cases

ADDITIONAL DIAGNOSTIC TESTS:

Virus isolation; immunofluorescent antibody assays; viral RNA detection using PCR; antigen detection using immunohistochemistry; serum virus neutralization; antigen capture ELISA
Skin biopsies are often used for IHC antigen detection because antigen is present in keratinocytes, hair follicle epithelium, and dermal papillae; cannot differentiate PI from acute infection

DIFFERENTIAL DIAGNOSIS:

Rinderpest (Paramyxoviridae, morbillivirus): Has both intranuclear and intracytoplasmic inclusion bodies as well as syncytia; declared eradicated worldwide in 2011
MCF: Malignant catarrhal fever (Herpesviridae, gammaherpesvirus): Similar gross findings, with additional conjunctivitis and corneal edema; histologically, if fibrinoid necrosis is present, BVD and MCF can be distinguished by looking at lymphoid organs; involution of lymphoid tissue occurs in BVD while lymphoproliferation occurs in MCF
IBR: Infectious bovine rhinotracheitis (Herpesviridae, alphaherpesvirus): Similar gross findings; also epithelial necrosis and intranuclear inclusions
Diseases with both oral lesions AND diarrhea: In North American bovids, BVD/MD and MCF are the two most common diseases with both of these symptoms
Diseases with oral lesions: Foot and mouth disease (Picornaviridae, aphthovirus); vesicular stomatitis (Rhabdoviridae, vesiculovirus); bluetongue (Reoviridae, orbivirus); bovine papular stomatitis (Poxviridae, parapoxvirus); necrotic stomatitis/oral necrobacillosis (Fusobacterium necrophorum), and malignant catarrhal fever (Herpesviridae, gammaherpesvirus)
Diseases with diarrhea: Salmonellosis, cryptosporidiosis, coccidiosis, coronavirus, rotavirus, paratuberculosis (Mycobacterium avium subsp. paratuberculosis), intestinal parasitism, arsenic poisoning, and copper poisoning
Other causes of pneumonia: Bovine respiratory syncytial virus, mannheimiosis, pasteurellosis, hemophilosis, or mycoplasmosis
Diseases that mimic the hemorrhagic syndrome: Septicemia with subsequent DIC, sweet clover poisoning, and bracken fern poisoning

COMPARATIVE PATHOLOGY:

Other pestiviruses of domestic animals:

Pigs – Classical swine fever; swine are also susceptible to bovine pestivirus (BVDV)
Sheep – Border disease virus; sheep are also susceptible to bovine pestivirus (BVDV)

REFERENCES:

Agnew, D. Camelidae In: Terio K, McAloose D, Leger J, eds. Pathology of Wildlife and Zoo Animals, San Diego, CA: Elsevier 2018:195-196.
Bianchi MV, Konradt G, de Souza SO, et al. Natural outbreak of BVDV-1d-induced mucosal disease lacking intestinal lesions. Vet Pathol. 2017;54(2):242-248.
Brodersen BW. Bovine viral diarrhea virus infections: Manifestations of infection and recent advances in understanding pathogenesis and control. Vet Pathol. 2014;51(2):453-464.
Carlson JM, Vander Ley BL, Lee SI, et al. Detection of bovine viral diarrhea virus in stable flies following consumption of blood from persistently infected cattle. J Vet Diagn Invest. 2020;32(1):108-111.
Durham AC, Boes KM. Bone Marrow, Blood Cells, and the Lymphoid/Lymphatic System. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022:844,882.
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